(1) Field of the Invention
The invention relates generally to light diffusing apparatus or flat light devices, which are widely used for general lighting or illumination, and for backlight illuminating passive type display devices such as liquid crystal display devices. More particularly, the invention relates to light diffusing apparatus or flat light devices utilizing an edge lighting effect in which light rays are repeatedly reflected between front and rear surfaces of a light transmission panel.
Furthermore, the invention generally relates to passive type display devices with light diffusing apparatus or flat light source devices for use in backlight illuminating passive type display devices and more particularly to passive type display devices having surface light source or flat light source devices utilizing the edge lighting effect.
(2) Description of Related Art
Liquid crystal displays are a typical example of passive type displays, which do not emit light by their selves, and this differs from active type displays, which emit light by their selves such as CRTs and electro luminescent devices. Accordingly, liquid crystal displays of the transmissible type, as opposed to the reflective type, are utilized in combination with a flat light source or light transmission panel for backlighting which is located in the rear of such displays, so that the display can be clearly viewed by a user in dark environments as well as bright environments.
Conventionally, such light transmission panels are widely used for the flat light sources as backlights or film viewers to illuminate the passive type displays such as liquid crystal displays of transmissible type or transparency films with visual information such as photographic transparency films or OHP (overhead projector) transparency films, by combination with light sources such as linear fluorescent lamps, located at side surface of the light transmission panel (i.e. positioned laterally the light transmission panel.)
This type of lighting system is called an xe2x80x9cedge lightingxe2x80x9d, or xe2x80x9clight transmission panelxe2x80x9d system, and the light transmission panel is made of transparent material with high light transmission characteristics such as acrylic resin and polycarbonate resin and glass. Light rays emitted from at least a light source are input to at least a side i.e. lateral surface of the light transmission panel. Such light rays are repeatedly reflected between front and rear surfaces in the light transmission panel. The light rays leak or are output gradually according to transmission of light rays to illuminate an object such as a liquid crystal display or a photographic transparency film.
The light transmission panel is ordinarily a panel or film having a rectangular surface area to be illuminated, which substantially corresponds to that of the liquid crystal display.
The light transmission panel for illumination has rectangular surfaces with two long sides and two short sides. There are following four types of the arrangement according to the positional relationships between the light transmission panel and the linear light source such as a linear fluorescent lamp:
(1) An arrangement in the short side-single light type in which a single linear light source is placed at a short side surface of the light transmission panel;
(2) An arrangement in the long side-single light type in which a single linear light source is placed at a long side surface of the light transmission panel;
(3) An arrangement in the short side-dual light type in which a linear light source is placed at each of the two short side surfaces of the light transmission panel; and
(4) An arrangement in the long side-dual lights type in which a linear light source is placed at each of the two long side surfaces of the light transmission panel.
As is well known in the field, light rays incident on the light transmission panel for illumination are transmitted inside the light transmission panel, and the light rays repeat internal total reflections from the light incident side to opposite side in the light transmission panel. Some quantity of transmitted light reaches the opposite side in the light transmission panel. The rest of the transmitted light leaks progressively from the surface of the light transmission panel for illumination to the outside of the light transmission panel to illuminate a passive type display or a photographic transparency film.
Accordingly, in the case in which the short side-single light type or long side-single light type is used, the brightness of a surface projecting from the surface of the light transmission panel is falls off rapidly according to the distance from the light source. Such single light types cannot produce uniform surface brightness and have lower surface brightness according to the distance from the light source. In the case in which a light transmission panel with a large surface area must be illuminated, the single light types cannot be used because the distance over which light is to be transmitted is too great and the brightness of the surface is extremely low near the opposite side terminal which is far from the light input side in the light transmission panel.
Therefore, the single light types are limited to use in color liquid crystal displays of small surface area or to use in monochrome displays not requiring relatively high and uniform surface brightness. The dual light types are used in color and monochrome liquid crystal displays with large surface areas requiring relatively high and uniform surface brightness, such as monitors or displays for personal computers or television receivers. In particular, portable electronic devices, driven by battery power sources and having liquid crystal displays with backlights, must be light in weight and compact, such as in notebook or palm-sized personal computers and information and telecommunication terminals. The dual light types using fluorescent lamps are not suitable for this purpose because the weight is almost double and space in the housing for accommodating the lamps is almost double compared to the single light type.
Fluorescent lamps have variable brightness and the emission at different locations on the lamp surface because, for example, blacking increases from the electrodes toward the center of the lamp over time, as is known in fluorescent lamps for general lighting purposes. Furthermore, the area blackened is increases over time and the area blackened differs from lamp to lamp. Therefore, in dual light types using fluorescent lamps, uniformity in brightness and color displayed at different points on the surface of the light transmission panel decreases over time compared to the single light type.
An object of the present invention is to provide a novel light diffusing apparatus including light guide means.
Another object of the present invention is to provide a novel light diffusing apparatus including light guide means capable of outputting light with a desired distribution of luminance or brightness.
Still another object of the present invention is to provide a novel light diffusing apparatus including light guide means capable of outputting light with substantially uniform distribution of luminance or brightness.
The light diffusing apparatus of the present invention can be suitably used in various optical devices such as surface light devices, light indicators, backlights or front lights of passive displays e.g. liquid crystal displays (LCDs) and vehicle lights.
The present invention includes a first light guide portion for light leakage i.e. light diffusion, a second light guide portion solely for light transmission and a third light guide portion for an optical communication with the first light guide portion and said second light guide portion. The first, second and third light guide portions may form substantially a single piece construction.
The first light guide portion may be comprised of a first side surface (i.e. a first end or a first end face) and the second light guide portion is further comprised of a second side surface (i.e. a second end or a second end face).
The present invention may be further comprised of at least one light generating device, in which the first and/or second side surfaces receive (i.e. accept) light emitting from the light-generating device.
The second and third light guide portions have at least a major surface and the major surface may have a light reflective layer. The light reflective layer may be composed of a transparent layer with lower optical refractive index than the second portion. Alternatively, the light reflective layer may be composed of a reflective metal layer.
The first light guide portion may have at least a first major surface and/or a second major surface and a light diffusing (i.e. light scattering) means disposed on the first light guide portion, for diffusing light from the first major surface and/or the second major surface.
The light diffusing means may be composed of a plurality of grooves (or projections) disposed on the first major surface and/or the second major surface and the grooves may form a pattern such as multiple dots or multiple stripes. The grooves may be formed by means of such as filing with an emery paper, sand blasting, chemical etching, laser irradiation or hot stamping.
Alternatively, the light diffusing means may be composed of a plurality of light diffusing layers disposed on the first major surface and/or the second major surface. The light diffusing layers may form a pattern such as multiple dots and/or multiple stripes.
The light diffusing layers may be formed by coating using painting material including multiple light diffusing powders, pigments or beads on the first major surface and/or the second major surface.
The first and second light guide portions may form substantially linear (i.e. planer) cross section, while the third light guide portion may form substantially non-linear cross section. The first light guide portion, second light guide portion and third light guide portion may form a U-shaped cross section as a whole; and each of the first light guide portion and the second light guide portion is a leg of the U-shaped cross section and the third light guide portion is a bottom of the U-shaped cross section.
A first aspect of the light diffusing apparatus includes single piece light guide means which have a single transparent panel-like member (or, sheet-like, plate-like or film-like member) and the transparent panel-like member has a first light guide portion for light leakage or light diffusion, a second light guide portion solely for light transmission and a third light guide portion for an optical communication with the first light guide portion and the second light guide portion, and the first, second and third light guide portions form substantially a single piece construction and have substantially a U-shaped construction as a whole.
The light diffusing apparatus based on the first aspect of the present invention may be manufactured according to following steps and following orders: a preparing step wherein a single panel-like member is so prepared that the first light guide portion has a first function for light transmission and light leakage, while the second and third light guide portions have a second function for solely for light transmission, in which the third light guide portions is positioned in an interim zone between the first light guide portion and the second light guide portion; a heating step wherein a heat is applied to at least the third light guide portions in order to sufficiently soften by means of a heater; a bending step wherein the third light guide portion is so bent during softening that the first and second portions are substantially parallel each other and the third portion has curved cross section; and a cooling step wherein the heat is removed so that the light diffusing apparatus keeps said U-shaped cross section in an ambient temperature.
A second aspect of the present invention includes a first light guide portion for light leakage or light diffusion, a second light guide portion solely for light transmission, a third light guide portion for an optical communication with the first light guide portion and the second light guide portion, wherein the first, second and third light guide portions form substantially a single piece construction; and wherein the first, second and/or third light guide portions are composed of at least a ribbon-like optical fiber cable having a first end and a second end and the ribbon like-like optical fiber cable is composed of a plurality of optical fibers parallel each other.
The ribbon-like optical fiber cable may have a linear or planer portion corresponding to the first and second light guide portions of the optical fiber cable and may have a non-linear or bent portion corresponding to the third light guide portion formed by bending an interim along a longitudinal length of the optical fiber cable. The first and second portions form linear cross sections, while said third portion forms a non-linear cross section, which is a bent or curved portion located at an intermediate section or zone between an end of the first light guide portion and an end of the second light guide portion.
Each one of the optical fibers of the second and third portions may have a core and a cladding to cover the core so as not to allow light leakage, in which refractive index of the core is higher than refractive index of the cladding, while each one of the optical fibers of the first portions may have a core and has not at least partially or entirely the cladding so as to allow light leakage.
Because the first, second and third light guide portions are a single piece construction, that is, a single unit in all the aspects of the present invention, an optical communication i.e. an optical coupling with the first and second light guide portions are very effectively carried out with minimum leakage of light transmission, as compared with the case in which all the first, second and third light guide portions are separated i.e. isolated and the transmission loss is very large between the second and third light guide portions and between the first and third light guide portions.